Do you really need to ask that? "We" have the land and the area for people, a lot of "the rest of the world" does not.

For other reasons, schooling and crime are such that for those that want families, cities are less than ideal than the suburbs. The ability to get around is relatively cheap.

And the economics reflect that. So you can anguish in your "what should be", but ultimately it mostly comes down to money and incentives.